1. Field of the Invention
This invention relates to a process for polymerization of 2,6-disubstituted phenol, more particularly to a process for producing a polyphenyleneether by oxidative polymerization of a 2,6-disubstituted phenol in the presence of a basic compound, a manganese compound and an N-alkylalkanolamine. According to the process of this invention, there is provided a polyphenyleneether with little undesirable coloration having excellent tensile strength and elongation. The polyphenyleneether also exhibits no deterioration in molecular weight when hot molded.
2. Description of the Prior Art
A polymer produced by oxidative polymerization of a 2,6-disubstituted phenol is known as a polyphenyleneether. In recent years, this polymer has received attention as a thermoplastic engineering plastic material because of its excellent mechanical properties, good electrical characteristics, good heat resistance, low absorbability of water and good dimensional stability.
For oxidative polymerization of a 2,6-disubstituted phenol, manganese catalyst system and copper catalyst system are known in the art. A large number of combinations of a copper salt or a manganese compound with various amines have hitherto been proposed in many patent publications. For example, Japanese Patent Publication No. 30,335/1970 describes various combinations of a manganese compound and a basic compound with a primary, secondary or tertiary amine. In such a combination, suitable amines include aliphatic primary amines such as methylamine, ethylamine, propylamine and butylamine and the like; cyclic hydrocarbon primary amines such as cyclohexylamine and the like; diamines such as ethylenediamine, triethylenediamine, hexamethyldiamine and the like; aliphatic secondary amines such as dimethylamine, diethylamine, dipropylamine, dibutylamine and the like; cyclic hydrocarbon secondary amines such as dicyclohexylamine and the like; alicyclic secondary amines such as piperidine, piperazine, morpholine, and the like; aliphatic tertiary amines such as trimethylamine, triethylamine, diethylmethylamine, dimethylpropylamine, dimethylethylamine, benzylmethylamine, dioctylbenzylamine, dioctychlorbenzylamine, (chlorophenethyl)bromobenzylamine, 1-dimethylamino-2-phenylpropane and the like; tertiary polyamines such as N,N,N', N'-tetraalkylphenylenediamines, N,N'-dialkylpiperidines, hexamethylenetetramine and the like; pyridines such as pyridine, picoline, cholidine and the like and cyclic amines such as N-alkylpyrole, N-alkylpyrolidine, N-alkylpiperidine, quinoline, isoquinoline, N-alkyltetrahydroquinoline, N-alkylmorpholine and the like. The disclosure of the aforesaid patent publication further mentions that these cyclic amine may include derivatives where one or more hydrogen atoms on a carbon atom member forming the heterocyclic nucleus is substituted by alkyl, alkoxy, or an isomeric or a homologuous group thereof.
However, the polyphenyleneether obtained using a primary amine as mentioned above does exhibit significant lowering in molecular weight upon melting by heating. Furthermore, the polymer has low-strength as well as low elongation in tensile test. With use of a secondary amine as mentioned above, the catalytic polymerization activity featured by a manganese compound-basic compound catalyst system is markedly lowered and such a catalyst system does not produce a high molecular weight polymer. Further, use of a tertiary amine as mentioned above, results in a brittle polymer which exhibits a reduction lowering in molecular weight when melted by heating.
It is also proposed in U.S. Pat. No. 4,083,828, to combine a secondary amine with a manganese salt and a basic compound. This combination also involves drawbacks similar to those mentioned before.
Further, a combination of a monoethanolamine or a diethanolamine or both with a manganese salt and a basic compound have also been described in Japanese Laid-open Patent Publication No. 44625/1982. However, a polymer obtained with use of ethanolamine still exhibits lowering in molecular weight when melted by heating, and low tensile strength and elongation. Moreover, the polymer, as molded, is brownish in color and thus undesirable for commercial use. With diethanolamines, such drawbacks as a poor resistivity of catalytic activity to the presence of water and lowered catalytic polymerization activity are encountered.
In addition to the above, the prior combination catalysts need use of large quantity of amine when used in combination with either a manganese compound or a copper salt.
In contrast to the catalyst containing an amine component, a bicomponent catalyst consisting of manganese compound and a basic compound, such as sodium hydroxide, is described in U.S. Pat. No. 3,573,257. Although the bicomponent catalyst produces a higher polymerization rate at low cost, it is very difficult to control the molecular weight of the polymer product because of an abrupt increase in molecular weight in the later stage of the polymerization reaction. In addition, the polymer obtained is very brittle and has the disadvantage of a poor thermal stability, i.e., the molecular weight of the polymer deteriorates upon melting by heating.
In view of the state of the art described above, the inventors have made extensive studies to develop a polymerization catalyst having high catalytic activity which can produce a little colored polyphenyleneether having a reduced tendency to exhibit a decrease in molecular weight when the polymer is melted by heating, and having excellent tensile strength and elongation. It has now been found that a catalyst comprising a combination of a manganese compound and a basic compound with a N-alkylalkanolamine can achieve the aforesaid object. This invention is based on this novel finding.